Code tips:

$actual_link = 'http://'.$_SERVER['HTTP_HOST'].$_SERVER['PHP_SELF'];
echo "Our URL: $actual_link<br><br>\n";

# the entire URL of the current page, including query string
$url = $_SERVER['REQUEST_URI'];
echo "\$_SERVER['REQUEST_URI'] ---> $url<br><br>\n";

# the base URL of the current page without query string
$url_base = $_SERVER['PHP_SELF'];
echo "\$_SERVER['PHP_SELF'] ---> $url_base<br><br>\n";

# The web host
$host = $_SERVER['HTTP_HOST'];
echo "\$_SERVER['HTTP_HOST'] ---> $host<br><br>\n";

# Just the path of the URL without the filename
$path = substr($_SERVER['REQUEST_URI'], 0, strrpos($_SERVER['REQUEST_URI'], '/') + 1);
echo "Path of the URL without the filename ---> $path<br>\n";

More info on parsing the URL: http://php.net/manual/en/function.parse-url.php

Showing errors:

<?php
ini_set('display_errors', 1);
ini_set('display_startup_errors', 1);
error_reporting(E_ALL);
?>

test

<?php
echo "test<br>\n";
$file=fopen("welcome.txt","r");
?>